The chemical element lithium has been
found for the first time in material ejected by a nova. Observations of
Nova Centauri 2013 made using telescopes at ESO’s La Silla Observatory,
and near Santiago in Chile, help to explain the mystery of why many
young stars seem to have more of this chemical element than expected.
This new finding fills in a long-missing piece in the puzzle
representing our galaxy’s chemical evolution, and is a big step forward
for astronomers trying to understand the amounts of different chemical
elements in stars in the Milky Way.

The light chemical element lithium
is one of the few elements that is predicted to have been created by
the Big Bang, 13.8 billion years ago. But understanding the amounts of
lithium observed in stars around us today in the Universe has given
astronomers headaches. Older stars have less lithium than expected [1], and some younger ones up to ten times more [2].

Since the 1970s, astronomers have speculated that much of the extra lithium found in young stars may have come from novae
— stellar explosions that expel material into the space between the
stars, where it contributes to the material that builds the next stellar
generation. But careful study of several novae has yielded no clear
result up to now.

A team led by Luca Izzo (Sapienza University of Rome, and ICRANet, Pescara, Italy) has now used the FEROS instrument on the MPG/ESO 2.2-metre telescope at the La Silla Observatory, as well the PUCHEROS spectrograph on the ESO 0.5-metre telescope at the Observatory of the Pontificia Universidad Catolica de Chile in
Santa Martina near Santiago, to study the nova Nova Centauri 2013
(V1369 Centauri). This star exploded in the southern skies close to the
bright star Beta Centauri in December 2013 and was the brightest nova so
far this century — easily visible to the naked eye [3].

The very detailed new data revealed the clear signature of lithium
being expelled at two million kilometres per hour from the nova [4]. This is the first detection of the element ejected from a nova system to date.

Co-author Massimo Della Valle (INAF–Osservatorio Astronomico di
Capodimonte, Naples, and ICRANet, Pescara, Italy) explains the
significance of this finding: “It is a very important step forward.
If we imagine the history of the chemical evolution of the Milky Way as a
big jigsaw, then lithium from novae was one of the most important and
puzzling missing pieces. In addition, any model of the Big Bang can be
questioned until the lithium conundrum is understood.”

The mass of ejected lithium in Nova Centauri 2013 is estimated to be
tiny (less than a billionth of the mass of the Sun), but, as there have
been many billions of novae in the history of the Milky Way, this is
enough to explain the observed and unexpectedly large amounts of lithium
in our galaxy.

Authors Luca Pasquini (ESO, Garching, Germany) and Massimo Della
Valle have been looking for evidence of lithium in novae for more than a
quarter of a century. This is the satisfying conclusion to a long
search for them. And for the younger lead scientist there is a different
kind of thrill:

"It is very exciting,” says Luca Izzo, “to find something that was predicted before I was born and then first observed on my birthday in 2013!”

Notes

[1] The lack of lithium in older stars is a long-standing puzzle. Results on this topic include these press releases: eso1428, eso1235 and eso1132.

[2] More precisely, the terms
“younger” and “older” are used to refer to what astronomers call
Population I and Population II stars. The Population I category includes
the Sun; these stars are rich in heavier chemical elements and form the
disc of the Milky Way. Population II stars are older, with a low
heavy-element content, and are found in the Milky Way Bulge and Halo,
and globular star clusters. Stars in the “younger” Population I class
can still be several billion years old!

[3] These comparatively small
telescopes, equipped with suitable spectrographs, are powerful tools for
this kind of research. Even in the era of extremely large telescopes
smaller telescopes dedicated to specific tasks can remain very valuable.

[4] This high velocity, from the nova
towards the Earth, means that the wavelength of the line in the
absorption in the spectrum due to the presence of lithium is
significantly shifted towards the blue end of the spectrum.

More information

This research was presented in a paper entitled “Early optical spectra
of Nova V1369 Cen show presence of lithium”, by L. Izzo et al.,
published online in the Astrophysical Journal Letters.

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